1. Field of the Invention
The present invention relates to a drying apparatus for sheets of material, and includes drying chamber means through which a sheet of material which is to be dried is conveyed, and in which the sheet of material is contacted by flowing drying gas; the apparatus also includes a feed line for supplying drying gas to the apparatus, a heater for heating the drying gas, and a withdrawal line for withdrawing the drying gas from the apparatus.
2. Description of the Prior Art
Drying apparatus of this general type are known, and are used, for example, for removing the solvent from solvent-containing pasty coatings for commercial adhesive material and strip-like medicinal bandage material.
During the manufacture of sheets of coated products which are impregnated with medicine (transdermal therapeutic systems, TTS), drying problems occur. Heretofore known constructions of drying apparatus are suitable to only a limited extent for overcoming these problems.
During recent decades, effort has been directed at achieving the greatest possible drying effect with the shortest possible overall length, and with the most accurate control. This is generally achieved by circulation of partial streams of the drying gas within the dryer sections. The great drawback connected herewith is that the inner surfaces of the drying apparatus, which come into contact with the substances, including medicine, which escapes form the sheet of material which is being dried, are unusually complicated and have a large number of dead spaces, undercuts that are not very accessible for cleaning, and even nearly completely closed-off hollow spaces (pipes, blowers, nozzles, etc.). An effective cleaning of the drying apparatus is particularly necessary when the apparatus is used for the successive drying of sheets of material which are coated with different medicines. A contamination of such material with medicine residue from a previous drying charge is not acceptable, especially when the medicines have opposing effects. When smaller charges of sheets of material having special medicines, for which only a limited requirement exists, are to be dried, it is important to be able to undertake the cleaning in a short period of time in order to avoid down times. Furthermore, for reasons of hygiene, residues of medicine cannot be allowed to pass into the atmosphere of the work location. Finally, the sheets of material which are to be dried cannot be allowed to be contaminated by external contaminants, such as dust particles and bacteria.
An object of the present invention is to provide a drying apparatus of the aforementioned general type which enables a rapid and effective drying of sheets of material without contamination from residues of previous charges and/or from contaminants in the external atmosphere; the drying apparatus should also prevent escape of substances from the sheets of material into the atmosphere.